Control of Sexually Dimorphic Brain Pathway Development in Cultured Zebra Finch Brain Slices
Holloway, Carl Clayton, III
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Permalink
https://hdl.handle.net/2142/86746
Description
Title
Control of Sexually Dimorphic Brain Pathway Development in Cultured Zebra Finch Brain Slices
Author(s)
Holloway, Carl Clayton, III
Issue Date
1999
Doctoral Committee Chair(s)
Clayton, David F.
Department of Study
Microbiology
Discipline
Microbiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Neuroscience
Language
eng
Abstract
In zebra finches (Taeniopygia guttata), males sing but not females. Previous studies showed singing requires the formation of a male-specific projection from nucleus HVC (higher vocal center, in the neostriatum) to nucleus RA (robust nucleus of the archistriatum). Fibers from HVC first enter the male RA about day 30 post-hatch, and extend toward but never enter the female RA except in birds given estrogen implants, in the first 1--3 weeks of life. The signals and mechanisms responsible for the abrupt ingrowth of HVC fibers into RA at ∼4 weeks are unknown. This thesis describes the development of a zebra finch brain slice culture system, and its application to identify the signals controlling formation of the HVC-RA pathway. Using a stationary culture method and a semidefined medium, metabolically active slices from adult brains were maintained for six weeks. Tract tracing, using the lipophilic dye DiI, demonstrated HVC-RA fibers were also maintained in these long-term cultures. Next, slices from males at 25 days of age (just before HVC-RA pathway formation) were placed in culture. From 1--3 weeks in vitro, these male slices developed a robust fiber projection from HVC, and the terminals of these fibers filled a topographic area equivalent to RA in uncultured adult control sections. Female slices of the same age developed a fiber projection from HVC in the same direction, but the terminals of these fibers labeled a significantly smaller area and avoided the central portion of RA. Addition of estrogen to the medium induced a male-like pattern of pathway development in female slices. By contrast, addition of estrogen inhibitors (tamoxifen or fadrozole) induced a female-like pattern of development in male slices. Direct exposure of female to male slices resulted in male-like development in both. Direct measurements of estrogen levels through enzyme-linked immunoassays of conditioned medium showed male slices are producing substantial levels of estrogen, even after 18 days in culture. Estrogen was detected in some female slices but at an average four-fold lower level. From these results we conclude male brains must produce estrogen locally and autonomously, and this estrogen is necessary and sufficient to trigger ingrowth of fiber terminals from HVC into the core of RA.
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